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  • STRUCTURAL MECHANICS  (5)
  • INSTRUMENTATION AND PHOTOGRAPHY  (3)
  • 1980-1984  (8)
  • 1
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    Application Explorer Mission 2 (AEM 2), Stratospheric Aerosol and Gas Experiment (SAGE) (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA, Washington Upper Atmosphere Res. Program; p 234-235
    Format: text
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  • 2
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    Digital multishaker modal testing (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A review of several modal testing techniques is made, along with brief discussions of their advantages and limitations. A new technique is presented which overcomes many of the previous limitations. Several simulated experiments are included to verify the validity and accuracy of the new method. Conclusions are drawn from the simulation studies and recommendations for further work are presented. The complete computer code configured for the simulation study is presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-170951 , NAS 1.26:170951 , CAR-83-1
    Format: application/pdf
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  • 3
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    A substructure coupling procedure applicable to general linear time-invariant dynamic systems (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A substructure synthesis procedure applicable to structural systems containing general nonconservative terms is presented. In their final form, the nonself-adjoint substructure equations of motion are cast in state vector form through the use of a variational principle. A reduced-order mode for each substructure is implemented by representing the substructure as a combination of a small number of Ritz vectors. For the method presented, the substructure Ritz vectors are identified as a truncated set of substructure eigenmodes, which are typically complex, along with a set of generalized real attachment modes. The formation of the generalized attachment modes does not require any knowledge of the substructure flexible modes; hence, only the eigenmodes used explicitly as Ritz vectors need to be extracted from the substructure eigenproblem. An example problem is presented to illustrate the method.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-178510 , NAS 1.26:176144 , CAR-84-1
    Format: application/pdf
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  • 4
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    Modal analysis using a Fourier analyzer, curve-fitting, and modal tuning (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The proposed modal test program differs from single-input methods in that preliminary data may be acquired using multiple inputs, and modal tuning procedures may be employed to define closely spaced frquency modes more accurately or to make use of frequency response functions (FRF's) which are based on several input locations. In some respects the proposed modal test proram resembles earlier sine-sweep and sine-dwell testing in that broadband FRF's are acquired using several input locations, and tuning is employed to refine the modal parameter estimates. The major tasks performed in the proposed modal test program are outlined. Data acquisition and FFT processing, curve fitting, and modal tuning phases are described and examples are given to illustrate and evaluate them.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-161886 , CAR-81-1
    Format: application/pdf
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  • 5
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    Modal vector estimation for closely spaced frequency modes (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Techniques for obtaining improved modal vector estimates for systems with closely spaced frequency modes are discussed. In describing the dynamical behavior of a complex structure modal parameters are often analyzed: undamped natural frequency, mode shape, modal mass, modal stiffness and modal damping. From both an analytical standpoint and an experimental standpoint, identification of modal parameters is more difficult if the system has repeated frequencies or even closely spaced frequencies. The more complex the structure, the more likely it is to have closely spaced frequencies. This makes it difficult to determine valid mode shapes using single shaker test methods. By employing band selectable analysis (zoom) techniques and by employing Kennedy-Pancu circle fitting or some multiple degree of freedom (MDOF) curve fit procedure, the usefulness of the single shaker approach can be extended.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-162001 , NAS 1.26:162001 , CAR-82-1
    Format: application/pdf
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  • 6
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    A substructure coupling procedure applicable to general linear time-invariant dynamic systems (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A substructure synthesis procedure applicable to structural systems containing general nonconservative terms is presented. In their final form, the non-self-adjoint substructure equations of motion are cast in state vector form through the use of a variational principle. A reduced-order model for each substructure is implemented by representing the substructure as a combination of a small number of Ritz vectors. For the method presented, the substructure Ritz vectors are identified as a truncated set of substructure eigenmodes, which are typically complex, along with a set of generalized real attachment modes. The formation of the generalized attachment modes does not require any knowledge of the substructure flexible modes; hence, only the eigenmodes used explicitly as Ritz vectors need to be extracted from the substructure eigenproblem. An example problem is presented to illustrate the method.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 84-0944
    Format: text
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  • 7
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    Multishaker modal testing (1983)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Procedures for improving the modal modeling of structures using test data and to determine appropriate analytical models based on substructure experimental data were explored. Two related research topics were considered in modal modeling: using several independently acquired columns of frequency response data, and modal modeling using simultaneous multi-point excitation. In component mode synthesis modeling, the emphasis is on determining the best way to employ complex modes and residuals.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-170952 , NAS 1.26:170952 , CAR-83-2
    Format: application/pdf
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  • 8
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    State vector formulation of substructure coupling for damped systems (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A generalized substructure coupling procedure in state vector form is derived for a complex system with general viscous damping. This first-order differential equation formulation is used in order to permit complex substructure modes to be employed easily. The free-interface normal (complex) modes and rigid-body modes of the substructure are defined. Complex residual attachment modes which result from static approximation of neglected higher modes are derived. The motion of each substructure is represented by a selected set of component modes. Equations of interface compatibility are employed to obtain an independent set of system equations of motion. A new method which employs incomplete complex normal modes in conjunction with the complex residual attachment modes to account for the contribution of neglected higher order modes is derived. Examples are employed to indicate how a damped structure may be analyzed by including the effect of residual attachment modes. Numerical results indicate that the new component mode synthesis method provides sytem equations of motion with reduced number of degrees of feedom leading to more accurate approximations to the system frequencies and damping factors than are obtained by pure mode truncation.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 83-0965 , Structures, Structural Dynamics and Materials Conference; May 02, 1983 - May 04, 1983; Lake Tahoe, NV
    Format: text
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